(classical particle similar to 於|于[yu2]) in; at; from; because; than;
Depicts wind rustling through a tree branch (丂). Based on the original meaning "exhale, shout", now written as 呼. The current meaning is a phonetic loan.
《說文》:“乎,語之餘也。从,象聲上越揚之形也。”
exhale, shout